It's notable for its compatible with Kotobukiya's other lines of model kit. The mech is highly customizable, both in real life and plot.
Although this isn't based on anime, Kotobukiya does provide us with background storyline on each mech, which reflect bits of the world they are in.Frame Architect Type 001Profile
Originally designed to be labor machine in grand scheme known as Project Re Sphere. After 10 years of trial and error, they finally get Frame Architect 001 which can mimic human movement perfectly and can use in all environment by swapping parts. However, Project Re Sphere never get launch and Frame Architect got adapt as weapon known as Frame Arms (FA) instead. This is the frame skeleton of everything else below.SA-16 StyletProfile
The first generation FA for aerial combat, based on labor model call S-10 Still. It has lightweight because of new armor material known as Julanium. Design for high-speed dogfight, there are G-force damper and balancer/stabilizer all over its body. The wheel heels are actually landing gears, with combination of Seiren Mk.2 engine on its back, Stylet is capable of STOL.
Originally there are 12 prototype YSA-16. The production model has inferior performance, but has same appearance. Standard armaments are 60 mm gatling gun and 2 missiles, both mount on forearm. Its production license spread world wide.Type 32 Model 1 GouraiProfile
The first generation FA, design to replace main battle tank by Japanese Force. Its heavily composite Julanium armor has built-in generator, providing strength to overcome the additional weight. There are tank thread on its calfs, these will be use to increase speed on proper terrain. Its main armament is 120mm recoilless cannon on right shoulder. This cannon is on turret and can adjust its fire arc to certain degree. There is sensor on Gorai's left shoulder which link to this turret. It also has tactical knife for close combat. However, Gourai is pretty much based on pure theory but did much worse in actual combat. Most of available Gourai got field modification from their pilot in order to fight effectively.

SA-16d KhanjarProfile
During Ant invasion, Middle East defense force purchase Stylet from France. While Stylet does has speed to response against Ant attack (Middle East has large teritory to cover), its did poor on ground and need to remain airborne. So Stylet has too short operational period and can't use for ground holding. This lead to development of Khanjar. Take advantage of Stylet's lightweight, Khanjar use reverse joint legs to increase its running speed. And can use the landing gears to dash in proper terrain. The stabilizers are removed. Khanjar has secondary engine on each shoulder to keep its aerial mobility on par with Stylet. Since the propulsion system consume much of energy, Khanjar can't use laser weapon effectively. The standard armaments switch to handhold mid-machine gun and multi-missile launcher. Khanjar proved to be veryeffective model, leading to success of Operation Ant Cleaner. USA Special Force adopt Khanjar, call it "Ostrich" instead while France use Khanjar as the base model for their in-development "Super Stylet".

Type 32 Model 5 SenraiProfile
Improvement over Gourai in respond to Ant attack, as Gourai turn out to be highly ineffective, especially when taking defensive role or fighting in urban environment. It has improved main sensor. The cockpit was switch to double seat type for pilot and operator (it still need only a pilot to operate). Chest armor was reinforced to provide better protection. Focus on close combat, Senrai has stunt knuckle on its left hand. This weapon is greatly effective against Ant unmanned FA by deliver electric discharge to burn Ant's AI circuit. Standard handhold weapon is double barrel gun (said to be used by USA FA force). It has option to attach with either chainsaw or laser bayonet. Since the tank threads are removed, Senrai will use transport helicopter to deploy at long distance.

That is all I found and manage to translate (ok, not very good translation either). Kotobukiya did reveal two mor FA, but yet to has their profile on official page.Type 38 Model 1 Ryurai KaiRF-9 Revenant Eye
I must note that both of them are loaded with more equipments or gimmick when compare to previous kits.

Hmm, I think there is manga based on this series but info is still lacking.

I believe new profile for Revenant Eye will coming soon, but here is one for Ryurai Kai.

Originally designed as long range support unit for Gourai, Ryurai was armed with long range plasma solid cannon on each shoulder. The cannons can adjust their angle and shoot in arc to hit target at close range (like mortar). There is reinforce armor with stabilizer from knees below, to increase its stability while shooting the cannons. Ryurai is notable for high agility in comparision to other support unit (guess they mean ballistic tank), yet suppose to remain in backline.

When they put the design in use, however, the Ryurai's pilot often found himself in frontline since Gourai is lacking at firepower. So they refine the Ryurai as Ryurai Kai (and assign model number Type 38 to it). The improvement are optical sensor on head and large bulletproof shield on each shoulder (which also use to store a tactical knife). Provide Ryurai with better defense in heat of battle. It's success model, typical Japan FA battalion is often consist of both Gourai and Ryurai Kai in single squad.

By the way, Gourai and its successors are adopted by USA force. Gourai is known as M-32 Werewolf while Ryurai Kai is M-38 Werewolf Blooper. Senrai was limited to experimental model though, known as M-322 Werewolf Fang.